dt-bindings: mfd: hisilicon,hi6421-spmi-pmic: Clean up example

dt-bindings: mfd: hisilicon,hi6421-spmi-pmic: Clean up example

The SPMI PMIC sits on an SPMI bus which and has two address cells with
no size.

Clean up the example by adding a parent SPMI bus node with proper
'#address-cells' and '#size-cells' properties, using a define for the
second register value, dropping the unnecessary label and increasing the
indentation to four spaces.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231206111754.7410-4-johan+linaro@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>